Directional couplers have many applications. A microstrip directional coupler is a 4-port radio frequency (RF) device based on a printed circuit board with two copper plated sides. Copper plating on the bottom side of the board is intact and serves as ground return path for all 4 ports of the microstrip directional coupler. The copper plating on the top side of the board is formed into two parallel traces. The advantage of microstrip line technology is simplicity and high repeatability. A typical microstrip line based directional coupler utilizes edge electromagnetic (EM) coupling between two copper traces. The width of the traces determines the characteristic impedance of the traces. The length of the traces determines the frequency of operation. The distance between traces determines the coupling factor. The closer the traces to each other the tighter is the coupling between them. Loosely coupled microstrip directional couplers are used to monitor incident and reflected RF signal flow. Other applications include retrieving a sample of incident RF signal for automatic gain/power control at the output of the RF transmitter. Reflected RF signal sample can be used to estimate a voltage standing wave ratio (VSWR) of the antenna feed and used to protect RF transmitter from inadvertent device failure when reflected signal is too high.